Friedrich Hund [Friedrich Hermann Hund] was a German physicist born on February 04, 1896 – died on March 31, 1997. Hund was made pivotal contributions to quantum theory. Hund discovered the so-called tunnel effect or quantum tunneling and Hund's rule of maximum multiplicity.
He also did significant work on the structures of atoms and molecules. Hund helped introduce the method of using molecular orbitals to determine the electronic structure of molecules and chemical bond formation.
Quantum Tunneling
Quantum tunneling refers to the quantum mechanical phenomenon where a particle tunnels through a barrier that it classically could not surmount. Quantum tunneling plays an essential role in several physical phenomena, such as the nuclear fusion that occurs in main sequence stars like the Sun. It has important applications to modern devices such as the tunnel diode, quantum computing, and the scanning tunneling microscope.
Friedrich Hund was the first to take notice of tunneling in 1927 when he was calculating the ground state of the double-well potential. Its first application was a mathematical explanation for alpha decay
Hund's Rule of Maximum Multiplicity
Hund's rule of maximum multiplicity is an observational rule which states that a greater total spin state usually makes the resulting atom more stable. The multiplicity of a state is calculated as the total number of unpaired electrons + 1, or twice the total spin + 1 written as 2S+1. A high multiplicity state is therefore the same as a high-spin state. The increased stability of the atom, most commonly manifested in a lower energy state, arises because the high-spin state forces the unpaired electrons to reside in different spatial orbitals.
Read More: Friedrich Hund – discoverer of Hund’s rule
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